Method of preparing stable NiOOH

ABSTRACT

Stable NiOOH is prepared by mixing an alkali metal hydroxide with nickel hydrate and ozonating the resultant mixture.

United States Patent Megahed et a1.

METHOD OF PREPARING STABLE NIOOH Inventors: El Sayed Megahed, Madison;

Patrick J. Spellman, Middletown, both of Wis.'. Leif Tennare, Lund,

Sweden Assignee: ESB Incorporated, Philadelphia, Pa.

Filed: Jan. 28, 1974 Appl. No; 437,233

us. (:1. 423/592; 136/29; 136/137 [111. c1 ,1 COlg 53/04 Field of Search .1 423/592; 136/29, 137

References Cited UNITED STATES PATENTS 1/1914 Edisun 423/592 X Primary ExaminerHerbert T, Carter [57] ABSTRACT Stable NiOOH is prepared by mixing an alkali metal hydroxide with nickel hydrate and ozonzlting the resu1- *anl mixture,

9 Claims, 2 Drawing Figures US. Patent 0m. 7,1975 Sheet 1 of 2 3,911,094

GASSING OF NiOOH KOH ADDED TO Ni(OH) (before ozoncnion) O /o (CONTROL) GASSING RATES (cc/gm) TIME(Dclys) Fig I U.S. Patent 0a. 7,1975 Sheet 2 0f 2 3,911,094

H mm m FOm O m Z G@ Nw A GK O (CONTROL) 2 33 WEE @2593 TIME Days) METHOD OF PREPARING STABLE NIOOH BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a method for preparing stable NiOOH by mixing an alkali metal hydroxide with a nickel hydrate and ozonating the resultant mixture. More particularly, the nickel hydrate is mixed with potassium hydroxide. sodium hydroxide. lithium hydroxide, rubidium hydroxide or cesium hydroxide and the resultant mixture is then dry ozonated. The resultant stable NiOOH is a useful cathodic material in both primary and secondary batteries.

2. Description of the Prior Art The nickel zinc couple has been the subject of extensive investigation and experimentation in the last several years. Recent work has indicated possible recharging of the system, and the proven long life capabilities of the nickel electrode combined with the high rate and energy density of the zinc electrode result in a practical high energy secondary battery. There has been, however, little commercial success in the area of primary nickel-zinc cells and the principal reason for this lack of success has been the instability of the nickel oxyhydroxide utilized as a cathodic material in such cells. The form of nickel oxide generally utilized in these primary cells has been trivalent nickel oxyhydroxidc which is commonly produced by such methods as the electrochemical oxidation of nickel hydroxide and alkaline electrolyte based on KOH as the major component or the ozonation ofnickel-ll hydroxide at a temperature of from to l 10C. Such trivalent nickel oxyhydroxide will, however, when contacted with alkaline solutions. give off oxygen according to the following equation:

This evolved oxygen has a detrimental effect on cell capacity and capacity maintenance and additionally may 4 cause the cells in which it is used to bulge or even explodc.

It has recently become known that high-valency amorphous nickel oxides could be stablized at their high-valent state and could be successfully exploited faradaically thus permitting their use as a cathodic material in primary cells. Tetravalent nickel oxyhydroxide is now recognized as satisfying the requirements for use as a cathodic material in primary cells.

It has heretofore been disclosed that a stable tetravalent nickel oxyhydroxide can be prepared electrochemically; see for example Tuomi, Journal of the Electrochemical Society, January I965, pages I to 12. Tuomi in this article discloses the preparation oftetravalent nickel" by charging crystalline Ni(OH) at I milliamps for 17 days in a suitable electrolyte.

A novel method has now been discovered for the preparation of stable tetravalent nickel oxyhydroxide which tetravalent nickel oxyhydroxide is useful as a cathodic material in both primary and secondary battcr- 6 IQS.

SL'MMARY OF THE INVENTION This invention is directed to a method for preparing stable tetravalent nickel oxyhydroxide by mixing an alkali metal hydroxide with nickel hydrate and dry ozonating the resultant mixture.

DESCRIPTION OF THE DRAWINGS FIG. I is a graphic representation of the gassing rate of the stable nickel oxyhydroxide depolarizer prepared according to the method of this invention plotted against the time in days.

FIG. 2 is a graphic representation of the gassing rate of nickel oxyhydroxide depolarizer to which the metal hydroxide has been added subsequent to the ozonation of the nickel hydrate plotted against the time in days.

DESCRIPTION OF THE INVENTION A novel method has now been discovered for the preparation of stable tetravalent nickel oxyhydroxide which is an effective and efficient cathodic material for use in both primary and secondary batteries. If x in the formula Ni O, (nickel oxyhydroxide) is 3.0, the product is trivalent. Ifx in the formula is more than 3.0 then the product is at least partially converted to the tetravalent state. Ideally, a product wherein the value ofx is 4.0, i.e., the entire compound is in the tetravalent state. This is, however, the ideal' state and for the purposes of this invention the term tetravalent shall mean nickel oxyhydroxide wherein the value of .t' is more than 3.0.

In the process of this invention, a dry alkali metal hydroxide is mixed with the dry nickel hydrate, i.e., Ni- (OHJ and the resultant mixture is dry ozonated to produce stable tetravalent nickel oxyhydroxide.

The dry nickel hydrate is readily available commercially. By the term dry alkali metal hydroxide as used herein is meant a dry hydroxide of potassium, sodium, lithium, cesium, rubidium and mixtures thereof, potassium hydroxide being the preferred material. These metal hydroxides often contain bound water and for the purpose of this patent will be used as supplied by the manufacturers in a solid form. The amount of metal hydroxide mixed with the nickel hydrate is from about 5 to about 40 wt. percent based on the weight of the dry nickel hydrate. Depending upon the particular alkali metal hydroxide utilized in the preparation of the stable nickel oxyhydroxide, the useful concentration range for each of the metal hydroxides listed above are as follows:

Potassium hydroxide Sodium hydroxide Cesium hydroxide Rubidium hydroxide Lithium hydroxide The nickel hydrate and alkali metala hydroxide may be mixed by any method known in the art. For example, the dry nickel hydrate may be placed in a ceramic ball-mill and pellets of the selected alkali metal hydroxide may be ground into fine powder, e.g., in a mortar and pestle, and the ground metal hydroxide powder may be added to the nickel hydrate in the ball-mill. The mixture could then be ball-milled for about 30 minutes or until a fine powder is produced. The resultant fine powder may then be passed through a screen, e.g.. mesh, to eliminate large particles prior to ozonation.

The mixture obtained above would then be dry ozonated by an appropriate method, for example. the mixs ture could be transferred from the ball-mill to an Erlenmeyer flask and the flask could be rotated by a small motor while ozone is passed over the mixture in the rotating flask. The ozone oxidizes the nickel hydrate- The presence of the metal hydroxide is beneficial for this reaction to proceed as shown in Table 1.

Table 1 Effect of KOH Addition and Time of Ozonation on the Formation ol- Tri and Tetravalent Nickelic Oxide Valency of Nickel (x) in Ni. .O

End Product Time Nitol ll NiUQHlg-KOH of Starting Starting ()7on- Material ('olor Material Color ation Ni. .O when: of End M where of End tHrsi Product x Product .1 2.2326 Black 2.](170 Black 6 l-Jhtit) Black 2.2480 Black l2 2 7462 Black 2 7504 Black 24 2.9482 Black 3.0942 BlaclvCiray 3n 2.95m) Black 3.2022 Gray 48 2 )(lU-J Black 3.52U2 Gray 72 ZHKUI Black 3.5700 (iray "l hrcc hundred grams of NitUH are ball-milled ll\ a ceramic ball-mill and passed through l| mesh screen before uyonalion.

*Ninety grams of KUH 1K5. kOH. l5" H 01 are mixed with 300 grains of NilOH], in a ceramic ball-mill and passed through 50 mesh screen before ozonation.

The ozonation is continued until the mixture becomes gray in color indicating the attainment of a tetravelent state wherein the mean valency of the oxide exceeds 3.00. Ozonation may be conducted at room temperature, however. if it is desired to ozonate at cool temperature, the rotating flask may be immersed in a cold bath of running water. The resultant product is stable tetravalent nickel oxyhydroxide, which may be used effectively in cathode preparation for both primary and secondary batteries.

Size 725 and 825 primary cells could be prepared for example by incorporating into a typical cell of the appropriate dimensions. the cathode utilizing the stable nickel oxyhydroxide prepared according to the method of this invention. Such a cell has a two-part container comprising an upper section or cap which houses the negative electrode or anode and the lower section or cup which houses the positive electrode or cathode. Useful anode material include cadmium. indium, Zinc, magnesium. aluminum. titanium and manganese, cadmium, indium and zinc being preferred and gelled or semi gelled zinc being most preferred. The bottom cup may be made of any suitable material such as nickelplated steel. and the cap may likewise be made of any suitable material known in the art such as tin-plated steel. The cap is insulated from the cup by means of an insulating and sealing collar which may be made of any suitable electrolyte resistant material. such as highdensity polyethylene or neoprene and it may be integrally molded around the edges of the cap for insulating the cap from the can and also to constitute an airtight enclosure. The negative electrode is separated from the ILL) positive electrode by means of an electrolyte absorbent layer and a separator. The electrolyte absorbent layer may be made of electrolyte resistant highly absorbent substances such as matted cotton fibre. Such material is available commercially for example under the trademark "WebriF. The separator layer may be any suitable semi-permeable material such Viskon" or Dexter" regenerated cellulosic material.

A suitable cathode may be selected utilizing a stable nickel oxyhydroxide prepared according to the method of this invention. The particular cathode prepared will be dependent upon the type of cell being made and the use to which it is to be put. For example, in a typical 725 or 825 cell five parts of stable nickel oxyhydroxide may be dry mixed with one part of a carbon material, e.g., graphite for increasing the mixed conductivity. To that dry mix may be added V Teflon (Whitc0n8") to serve as a binder and a lubricant and 7.5% electrolyte prewet of S071 potassium hydroxide. These components could be mixed well in for example a Patterson- Kelley blender or Abbe mixer or any other mixing apparatus. After the mix becomes homogeneous, the cathode mix can be pelletized on appropriate apparatus. A pellet thus prepared could then be inserted into the lower section or cup of the cell where it would function as a positive electrode or cathode.

EXAM PLES The following examples are intended to be merely illustrative of the invention and not in limitation thereof. Unless otherwise indicated, all quantities are by weight.

EXAMPLE 1 Samples of nickel hydrate (Ni(OH) (total 50 grams) containing 1% Co(OH) were prepared. Potassium hydroxide pellets were ground into fine powder and added to each nickel hydrate sample in the amount of l. 5, l0, 15, 20. 25 and 30% by weight. The material was then ball-milled for 15 minutes and then ozonated for three hours at cool temperatures, i.e., about l5C in a Welsbach ozonator Model T-408.

Additional nickel hydrates samples were prepared and ozonated as above but without the addition of the potassium hydroxide. After ozonation, potassium hydroxide was added to the NiOOH as above in the amount of l, 5, l0, i5, 20, 25 and 30% by weight.

The ozonated mixtures prepared above were tested for gassing by placing one gram of each sample in a sep' arate 12cc centrifuge tube and filling the rest of the tube with 50% KOH. The tubes were placed in a glycol bath maintained at a constant temperature of l45. Triplicate tests were made on each sample. Gassing was observed by measuring the height of KOH solution and a pipette stoppered over the centrifuge tube. Gassing rates were expressed in terms of cc of gas for one gram of material per day on test. Moisture determinations were done by a Cenco moisture balance.

Data in Table 2 below indicate that the KOH addition in amounts of HM or greater before ozonation pro' duced an extremely stable nickel oxyhydroxide with greatly reduced gassing. The total gas collected for the untreated gram control was 3.06 cc/gm of nickel oxyhydroxide after one week on test.

When the KOH was added to nickel oxyhydroxide after ozonation, some reduction in gassing of the nickel oxyhydroxidc was obtained. For example. the total gas in a week was 1.97, 1.45 and l.l() cc/gm for l0. l5 and 20% KOH additives. respectively. FIGS. 1 and 2 show these effects.

Table 2 to constitute airtight enclosure. The negative electrode of the cell comprises a gelled or semi-gelled zinc. The zinc electrode is separated from the positive electrode by means of an electrolyte absorbent layer and a separator. The electrolyte absorbent layer is made of elec- Gassing Rates of NiOGH Treated with Various 5 i Am unt f K H hcfnrc n utter mn i n trolytc resistant. highly absorbent matted cotton fibres.

Total (.ias w sarator la 'er is V1skon. The de olarlLer w is m- KOH Time of KOH E\ol\ed at '/1 The p 9.; Addiuun (45F (Cc/gm/wk, Muiswrc serted into the cell in pellet form. one pellet per cell.

The dry cathode mix consisted of:

l Before Ozonation 236 L8 I 5 Before ()zonation 1.10 4.8 l() 5 parts oxyhydruxldc (N1 H) Ill Before Ozonation .45 7.2 l part graphite and to that dry mix the following were added:

20 Before Ozonauon .l5 1 L0 35 Bur-Um Ommmun '33 1 l Teflon (WhitcOn-S inches) to serve as a binder 30 Before Ozonation .l7 12.0 and a lubricant QR; 821111211: 41 I 5 7.5% (weight a of a 50% KOH 50% H O solution 10 After ()zonation 1.45 6.2 The above components were mixed well in a Patterson- 22: Kelley blender and after the six became homogeneous, L '1 s 35 m, Omnuliun 1,35 104 pellets were made of the cathode mix on suitable pellet- 0101mm izing apparatus. Each pellet weighed 1.69 or -0.01

) (0mm! 0 I gram. See Table 3 below for test results.

Table 3 Treatment Anode CC V Amperimpedance Cell Ht Expansion age Depolarizer Process Material (volts) (Amps) (ohms) (mils) After I Wk at 145F l Trivalent Ni(OH) PDR L72 L8 0.90 l0 NiOOH Ozonated Zn 2 Tetravalent I054 KOH added PDR L73 2.7 0.62 0-3 NiOOH m NltOH 1, Zn

then ozonated as in Ex. 1 3 Same as 2 Gel Zn l 76 3.4 0.50 l-3 4 Same as 2 PDR l 78 1.2 1.4 l.53

except 10% Zn LiOH.H,O is used 5 Same as 2 PDR L76 3.] 0.5l 0-3 except i064 Zn NaOH is used 6 Trivalent Same as 2 FOR L74 l9 0.7 10

NiOOH except l0?! Co(OH) is used 7 Trivalent Same as 2 PDR L74 .0 0.7 [0

NiOOH except I095 g( )2 is used PDR 7.nPowder line with 14% mercury to prevent Linc corrosion.

Surprisingly, however. concentrations of 10 to KOH added before ozonation according to the method of the present invention were unexpectedly effective in reducing gassing of the nickel oxyhydroxide. For example, the total gas evolved in a week was 0.45, 0.20 and 0.l5 ec/gm for 10, 15 and 20% KOH additives. respectively. See FIGS. 1 and 2 for graphic representations of these effects.

EXAMPLE 2 Cells size 725 were constructed and tested. Each cell has an outside diameter of 0.736 0.738 inches. a height of 0.210 0.230 inches and a volume of 0.095 cubic inches. The cell has a two part container comprising an upper section or cap which houses the negative electrode or anode and a lower section or cup which houses positive electrode or cathode. The bottom cup is made of nickel plated steel and the cap is made of tin plated steel. The cap is insulated from the cup by means of an insulating and sealing collar of polyethylene and is integrally molded around the edges of the cap for insulating the cap from the cap and also EXAMPLE 3 Cells size 825 were constructed in the same manner as the 725 size cells of Example 2 except the following dimensions were different:

Outside Cell .900 .905 inches (22.86-22.99 mm] Diameter: Cell Height; .ZIB .228 inches (5.54-5.79 mm! Volume: .l l6 cubic inches 190 cubic cm) Weight. 3 ounces (8.50 grams! Each polarizer pellet weighed [.79 or .0l gram. See Table 4 below for test results.

Table 4: 825 Size Cells In all instances Ni(OH) was ozonated to NiOOH in preparation of the cell dcpolarizer, but cells tested varied in that the following various additional depolarizer ture is from about to about 40 weight percent based on the weight of the nickel hydrate.

2. A method according to claim 1 wherein the alkali metal hydroxide is potassium hydroxide.

preparation Steps were mkml2 5 3. A method accordmg to claim 2 wherein the amount of potassium hydroxlde present in the mixture Control st 15% i5"? 15%;

No NaOH KOH Be( OH H Ca( ()H Addition Added Added Added Added Initial cell capacity 192 In 229 165 182 to UHUY Ctlboff voltage Percent capacity rc- 8H1) 87.5 9i. tention at 4 ks at I 13-50% Percent capacity re 55 ll 67.5 75.5 tention at l2 wlts at l l3-5ll'i Percent Capacity re- 8L5 92.0 93.0 67.0 70,1! tention at 2 yrs at RT 70Fl (ell ht. increase at .(JU8U .(llKJS .Utl3ll 4 wks at l lfl-SUJ (inchesl Cell hi. increase m 0150 .0005 .0035 ms .0|70

I: Wlts at l |3 5u' (inches) Cell hi. lnCt'LllSC All. .0100 .0005 .0020 .0120 .0130 2 yrs. at RT (70F) (inches) (I l Iii-509$ at l I3F and 50% relative humidity (2) Cells discharged at 300 ohms l6 H/D I As can be seen from the data above, primary cells uti- |s from about 5 to about 40 weight percent. lizing a NiOOH depolarizer prepared according to the 4. A method according to claim 1 wherein the alkali method of this invention, i.e., l5% NaOH or 15% KOH metal hydroxide is sodium hydroxide added before ozonation, display unexpectedly low de- 5. A method according to claim 4 wherein the grees of cell bulging and good capacity retention as a amount of sodium hydroxide present in the mixture is result of the unexpected NiOOH stability in the cell. from about 5 to about 30 weight percent.

The embodiments of the invention in which an exclu- 6- A method ccording to l im 1 wherein the alkali sive property or privilege is claimed are defined as fol metal hydroxide is lithium hydroxide. lows: 7. A method according to claim 6 wherein the l. A method for preparing stable tetravalent nickel amount of lithium hydroxide present in the mixture is oxyhydroxide, which method comprises mixing an alfrom about 5 to about 20 weight percent. kali metal hydroxide selected from the group consisting 8. A method according to claim 1 wherein the dry of sodium hydroxide, potassium hydroxide, cesium hyozonation is carried out at room temperature. droxide. lithium hydroxide and rubidium hydroxide 9. A method according to claim 1 wherein the ozonawith nickel hydrate and dry ozonating the resultant tion is carried out at about 15C. mixture. wherein the amount of alkali metal in the mix 

1. A METHOD FOR PREPARING STABLE TETRAVALENT NICKEL OXYHYDROXIDE, WHICH METHOD COMPRISES MIXING AN ALKALI METAL HYDROXIDE SELECTED FROM THE GROUP CONSISTING OF SODIUM HYDROXIDE, POTASSIUM HYDROXIDE, CESIUM HYDROXIDE, LITHIUM HYDROXIDE AND RUBIDIUM HYDROXIDE WITH NICKEL HYDRATE AND DRY OZONATING THE RESULTANT MIXTURE, WHEREIN THE AMOUNT OF ALKALI METAL IN THE MIXTURE IS FROM ABOUT 5 TO ABOUT 40 BY WEIGHT PERCENT BASED ON THE WEIGHT OF THE NICKEL HYDRATE.
 2. A method according to claim 1 wherein the alkali metal hydroxide is potassium hydroxide.
 3. A method according to claim 2 wherein the amount of potassium hydroxide present in the mixture is from about 5 to about 40 weight percent.
 4. A method according to claim 1 wherein the alkali metal hydroxide is sodium hydroxide.
 5. A method according to claim 4 wherein the amount of sodium hydroxide present in the mixture is from about 5 to about 30 weight percent.
 6. A method according to claim 1 wherein the alkali metal hydroxide is lithium hydroxide.
 7. A method according to claim 6 wherein the amount of lithium hydroxide present in the mixture is from about 5 to about 20 weight percent.
 8. A method according to claim 1 wherein the dry ozonation is carried out at room temperature.
 9. A method according to claim 1 wherein the ozonation is carried out at about 15*C. 